Armed Mexican drug smugglers ransacked a National Guard unit in the Arizona desert this week, contradicting immigrant advocates’ portrait of a U.S.-Mexico border crossed only by humble and desperate migrants in pursuit of the American dream.

The attack took place late at night in a portion of the Arizona-Mexico border near Nogales that is well known as a drug corridor. In fact, the 120-mile stretch of desert is the U.S. Border Patrol Tucson sector’s busiest for drug seizures. Last year alone, 124,000 pounds of narcotics were confiscated in the area.

Evidently aware that the U.S. National Guard is helping the overwhelmed Border Patrol man these remote portions of the border, the violent Mexican drug smugglers used force to assure their cargo made it safely into the country. The National Guardsmen were forced to retreat and eventually, the attackers scrambled back into Mexico.

This is not the first time these sophisticated Mexican drug cartels use force to penetrate the United States. In fact, they often team up with members of the Mexican military and criminal gangs to assure their valuable goods make it into the country. Sometimes they get individuals, supposedly pursuing a better life in America, to carry smaller loads in backpacks.

Hundreds of incursions by the Mexican military have been documented in the southern border since the late 1990s, with Border Patrol agents and local law enforcement officers regularly coming under gunfire attack. For years federal government officials denied the invasions, but fed up law enforcement officials in Texas took photos and provided other evidence.